The present invention relates to controlling fluid flow and, more particularly, to a method for generating dynamically controllable oscillatory fluid flow, in a simple and efficient manner, featuring the capability of producing a zero mean oscillatory fluid flow rate, and oscillation parameters of high frequency, up to about 1 kHz, high amplitude, and variable wave form, and corresponding device and system for implementing the method thereof.
Currently, an important application of generating oscillatory fluid flow is for achieving high levels of dynamically controllable fluid flow, where it has been shown that oscillatory fluid flow at a controllable mean flow rate, frequency, amplitude, and waveform, significantly improves the performance of aerodynamic objects such as aircraft wings. In particular, using dynamically controllable oscillatory fluid flow significantly improves aerodynamic behavior of an aircraft during take-off and landing, with regard to aircraft stability and flight efficiency, translating to improved safety and fuel savings, respectively.
Employing methods and/or devices based on generating dynamically controllable oscillatory fluid flow in a variety of applications, represents a substantial improvement over using currently known methods and/or devices for dynamically controlling fluid flow. For example, the commonly known method of `steady blowing`, based on non-oscillatory fluid flow, can be used for controlling flow separation, and features a powerful driver such as part of a jet engine, for generating very high constant and uniform flow rates having essentially no amplitude. This method is limited by the need to use a very powerful driver for generating high flow rates. For similar types of aerodynamic applications of delaying flow separation, oscillatory blowing has zero mean flow rate, requiring only about 10 per cent of the momentum involved in steady blowing methods, in order to achieve the same affect of flow separation such as lift or drag.
Currently existing devices for generating oscillatory fluid flow include loudspeakers enclosed in a box, a T-valve, a disc valve, a disc valve featuring a membrane, and a piezoelectric (PZE) oscillator. These devices present a variety of significant limitations for achieving high levels of dynamically controllable fluid flow. They generate oscillatory fluid flow with a limited range of frequencies, and the amplitude of the oscillatory fluid flow decreases with increasing frequency. In some cases the oscillatory fluid flow is generated and superimposed on an existing non-oscillatory constant flow rate of high magnitude, impairing practical implementation for dynamic control of fluid flow. Attempts to solve those problems have usually resulted in cumbersome and operationally complex devices.
Loudspeakers enclosed in a box, used for generating oscillatory fluid flow of air, as taught by Nishri, doctoral dissertation, Tel Aviv University, Israel, 1995, is limited to oscillation frequencies less than 100 Hz, unless the device includes very large water cooled loudspeakers of diameter greater than 50 cm.
The T-valve, used for chopping air flow, developed by Sokolov and Bachar, 1992, and described by Seifert et al. in AIAA J., 31, 2052 (1994), is limited to oscillation frequencies less than 400 Hz.
The disc valve, also used for chopping air flow, developed by Seifert and Bachar, 1994, and disclosed by Hites et al., DFD97 APS Meeting, USA, 1997, enables generating oscillatory fluid flow having high frequencies. However, the oscillatory fluid flow is significantly limited by being superimposed onto an existing non-oscillatory constant flow rate having the same order of magnitude as the wave amplitude of the oscillatory flow. To solve the problem of interference due to the presence of the exiting constant flow rate, a membrane is added to the disc valve such as to enable separation between the constant and oscillatory flow components. Undesirably, however, the added membrane substantially attenuates the wave amplitude. It is also necessary to balance the pressure on either side of the membrane, in order to avoid membrane rupture. Moreover, additional problems can arise when using a membrane in a low-temperature environment, for example, during conditions of operating an aircraft.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method for generating dynamically controllable oscillatory fluid flow, in a simple and efficient manner, featuring the unique capability of producing a zero mean oscillatory fluid flow rate, and oscillation parameters of high frequency, up to about 1 kHz, high amplitude, and variable wave form, and corresponding device and system for implementing the method thereof.